The use of antimicrobial agents to treat and reduce oral and dental disease is well documented in the professional literature. Among the most efficacious such agents is ClO.sub.2, a strong oxidizing agent. ClO.sub.2 is well documented as a bactericidal, bacteriostatic, fungicidal, fungistatic, viricidal, and viralstatic agent. It is approved by the EPA under Registration Number 9048-3 for both water purification and food preparation and preservation because of this antimicrobial activity.
ClO.sub.2 is also effective in treating malodor. It achieves this efficacy by two mechanisms of action. First, ClO.sub.2 oxidizes the sulfide bonds of volatile and odoriferous sulfur compounds (specifically hydrogen sulfide and di-methyl mercaptan bonds) that are metabolic byproducts released by certain anaerobic bacteria documented to reside in the oral cavity; and second, its antimicrobial activity lowers the number of such microorganisms that release these volatile sulfur compounds.
However, because of its reactivity, ClO.sub.2 is unstable in an aqueous solution and, as such, cannot be stored at room temperature. Furthermore, since ClO.sub.2 is a gas, it cannot be stored in liquid form at room temperature. Thus, various references to "stabilized" ClO.sub.2 do not refer to gaseous ClO.sub.2, but rather to various chlorous acid-liberating compounds. Unfortunately, chlorous acid, even when buffered, will demineralize tooth enamel and lead to even more significant oral health problems.
One such chlorous acid-liberating compound used is sodium chlorite (NaClO.sub.2). References to the use of NaClO.sub.2 to generate chlorous acid can be found in the following papers: Chepek C W, Reed O K, Ratcliff Pa., Reduction of Bleeding On Probing With Oral Care Products, Compendium 1995, 16(2): 188-196; Bolin V, Ratcliff Pa., Germicidal Effect Of Providone Iodide and ClO.sub.2 On Dental Pathogens. J. Dent Res. 1987, 373. IADR Abstracts; Grootveld M, Silwood C, Lynch E., Ability of oral heathcare products to alleviate oral malodour. J Dent. Res. 1997; 289:50. IADR Abstracts.
Compositions for treating oral malodor that employ chlorine-containing compounds are disclosed in U.S. Pat. Nos. 5,772,986 to Richter; 5,738,840 to Kross; 4,552,679 to Schubel, and 4,808,389 to Ratcliff. These references disclose various vehicles for introducing the compositions to the oral cavity, including liquid rinses, toothpastes (either with or without suds), lozenges, and sprays, as disclosed in U.S. Pat. No. 4,837,009 to Ratcliff. The chemical mechanisms for producing compositions containing chlorous acid are varied. Some references, such as Ratcliff '215, describe the generation of chlorous acid at controlled pH levels using phosphate buffers. U.S. Pat. Nos. 4,891,216 to Kross and 4,902,498 to Agricola et al. disclose a two part system that generates chlorous acid by mixing a metal chlorite or other chlorous acid-liberating compound with a protic acid at acidic pH levels. U.S. Pat. No. 5,667,817 to Kross discloses a two-stage system that requires the use of lactic acid and that results in a composition having a very disagreeable taste, making it unsuitable for use in oral heathcare. As a consequence, this product is not commercially available. However, even those products that are commercially available have significant drawbacks due to their complex chemistries, poor shelf life, poor taste, and poor efficacy.
Because chlorous acid will form ClO.sub.2 in aqueous media, there will be some ClO.sub.2 generated whenever chlorous acid contacts water. However, no known product is able to consistently provide therapeutic levels of ClO.sub.2 capable of reliable and efficacious use, much less to do so in the presence of H.sub.2 O.sub.2. By employing a single-stage system, known products must control the spontaneous reaction that occurs between the metal chlorite and protic acid to form chlorous acid. For this purpose, various buffers must be used to regulate the system's pH below the pK.sub.a of chlorous acid, resulting in a relatively steady-state generation of chlorous acid. But, for these products to have any useful shelf-life, it is necessary that their steady-state ClO.sub.2 levels be fairly low. Furthermore, because the reaction is unidirectional, not only is the product's shelf-life determined by the amount of metal chlorite initially present in the system and its pH, but the end-user is unable to determine how much chlorous acid is present at any given time, as the amount of chlorous acid in the system decays over time.
Commercially available, non-chlorous acid-containing products, such as Mentadent.RTM. (active ingredients: baking soda and H.sub.2 O.sub.2) and Listerine.RTM. (active ingredients: thymol, eucalyptol, and methyl salicilate) oral rinses achieve plaque inhibition rates of only 15% and 30%, respectively. These levels are well below the therapeutic and prophylactic benchmark of about 50% plaque inhibition achieved by Peridex.RTM. oral rinse (active ingredient: chlorhexidine gluconate), which is available only by prescription. However, even though Peridex.RTM. is the most-effective, commercially available plaque inhibitor, it has serious drawbacks that limit its applicability. Most significant among these drawbacks is severe staining to hard oral tissues observed even with brief use. In addition to being unsightly, this black staining actually creates an environment for future plaque buildup, necessitating additional follow-up office visits to be removed by abrasion of the tooth surface, which, in turn, increases the teeth's susceptibility to caries.
There is a strong commercial need for a composite formulation that overcomes these problems. First, the ideal oral care composition would be available over-the-counter yet achieve plaque inhibition rates comparable to compositions currently available only by prescription, inhibit gingival inflammation and periodontal inflammation, reduce dental caries, and control oral malodor. Second, the ideal composition should provide equivalent or superior efficacy to known compositions, yet be pleasing to the taste, thereby increasing patient compliance. Third, the ideal composition should have a superior shelf life due to the chemical stability of the component reactants. Fourth, the composition should be easy to use and have a simple chemistry that reacts under normal environmental conditions (i.e., at ambient temperature and pressure and without the need for multiple steps, pressurized containers, etc.). Fifth, the composition once fully constituted should have a pH value that is suitable for oral use and not be harmful to the teeth or oral tissues. Sixth, the ideal composition should have an effervescent quality for increased aeration of the oral tissues to facilitate the reduction of anaerobic bacteria and other microbes. Seventh, the ideal composition should not stain the teeth, provide an environment for future plaque buildup, require additional treatment, or make the teeth more susceptible to caries. Finally, the ideal composition would enable the rapid, reliable, and predictable generation in situ of therapeutic levels of ClO.sub.2.